Technology described herein generally relates to aircraft flight management and, more particularly, relates to a method of computing aircraft engine throttle cutback during aircraft departure.
Aircraft are commonly equipped with a flight management system for managing aircraft flight control, generating flight profile data, and providing navigational information such as flight paths designated by waypoints that are represented by navigational location coordinates. Additionally, flight management control systems are also configurable to provide aircraft engine throttle settings for manual or automatic control of the engine thrust. During aircraft takeoff, a flight management system may determine engine thrust requirements to sufficiently elevate the plane on lift off from the runway such that the aircraft sufficiently climbs at a pitch rate, typically according to a programmed schedule or requirements set forth by the air traffic control.
Aircraft are typically equipped with jet engines capable of generating high levels of sound. Given the location of airports in close proximity to residential areas, the sound exposure levels (SEL) experienced within a nearby community due to aircraft departure have become an increasing issue which has lead to the implementation of noise abatement procedures to reduce the community noise during aircraft departures. More recently, the National Business Aircraft Association (NBAA) has attempted to establish a national standard for flight operations for noise abatement procedures. These procedures generally require that the aircraft, upon lift off from a runway during departure, climb at a maximum practical pitch rate to an altitude of one thousand feet above the runway airfield with flaps in a takeoff setting. Upon reaching the one thousand feet above field level, the procedures generally recommend that the aircraft accelerate to the final segment speed and retract the flaps. The procedures also recommend that the aircraft reduce the engine thrust to a quiet climb setting while maintaining a one thousand feet per minute climb rate and an airspeed not to exceed a defined speed until reaching an altitude of three thousand feet above field level. Above the three thousand feet level, the aircraft would resume the normal climb schedule with gradual application of climb power. Of course, the aircraft control would be subject to aircraft control requirements, and other airspeed limitations. Given differences with aircraft type and takeoff conditions, the aircraft pilot would have latitude to determine whether takeoff thrust should be reduced prior to, during, or after flap retraction.
The prior proposed noise abatement procedures typically employ fixed altitudes for thrust cutback and restoration, which typically results in aircrafts having different weights and different operating temperatures to be above different ground positions at the specified altitudes. For example, a heavy aircraft on a hot day will climb at a lesser pitch as compared to a lighter aircraft on a cold day. To ensure adequate noise reduction throughout the departure procedure, the thrust cutback and restoration altitudes are generally specified to be conservative, which results in a waste of fuel. It is generally recognized that a more efficient climb profile requires climbing with maximum uplift so that the aircraft spends less time at a low altitude where the drag coefficient is typically higher.
Additionally, with the prior proposed noise abatement procedures, a specified one thousand feet per minute climb rate is intended to provide the most thrust reduction possible and yet maintain a safe level of performance. However, depending upon the aircraft, the noise reduction realized with the power setting to achieve a one thousand feet per minute climb rate may be less than needed for compliance with the community ground noise limit. The actual noise footprint on the ground typically is a function of engine thrust setting, aircraft speed, and aircraft altitude above the ground. If engine thrust is reduced only enough to meet the required sound exposure level under current flight conditions, then a higher climb rate might be possible resulting in less time at lower altitude, and thus reducing drag and improving fuel economy.
Accordingly, it is therefore desirable to provide for an aircraft departure procedure that provides adequate noise reduction during the aircraft departure within the community noise standards, while enhancing fuel economy. It is further desirable to provide for a flight management system and method that efficiently manages the departure of an aircraft while providing optimal engine thrust cutback to efficiently achieve community noise abatement.